1. Field of the Invention
The present invention relates to a light emitting device and an electronic apparatus having a self light-emitting element.
2. Description of the Related Art
In recent years, a light emitting device including a light emitting element typified by an EL (Electro Luminescence) element has been developed. Wide use thereof is expected by making use of advantages such as high image quality, a wide viewing angle, a thin type, and a light weight because of a self light-emitting type. In general, a light emitting element is an element of a current drive type, and a current value flowing through a light emitting element and luminance of the light emitting element are almost proportionate to each other. Therefore, there is a display apparatus which adopts constant current drive that flows a constant current to a light emitting element (for example, see Patent Document 1).
Further, a light emitting element has a temperature dependence; when a surrounding temperature (hereinafter also referred to as an ambient temperature) is high, the resistance value decreases while in a low temperature, the resistance value increases. Moreover, a light emitting element has a characteristic of degrading along with time so that the resistance value increases by degradation with time (hereinafter also referred to as time degradation). Therefore, there is a light emitting device which controls an effect by a change of ambient temperature and time degradation of a light emitting element (for example, see Patent Document 2).
A light emitting device described in Patent Document 2 has a light emitting element, a power supply line, a buffer amplifier, a light emitting element for monitoring, and a constant current source. Constant current is supplied from the constant current source to the light emitting element for monitoring. When a change of ambient temperature and time degradation occur, the current value of the light emitting element for monitoring is not changed, while a potential of one electrode of the light emitting element for monitoring is changed. One electrode of the light emitting element for monitoring is connected to the power supply line through the buffer amplifier so that a potential of the power supply line is also changed when a potential of one electrode of the light emitting element for monitoring is changed in accordance with a change of ambient temperature and time degradation. Further, by changing a potential of a power supply line in accordance with a change of ambient temperature and time degradation, a light emitting device described in Patent Document 1 can control an effect by a change of resistance value of a light emitting element due to a change of ambient temperature and time degradation.
[Patent Document 1] Japanese Patent Laid-Open No. 2003-323159
[Patent Document 2] Japanese Patent Laid-Open No. 2002-333861